package common;
/*
 * Copyright (c) 1995, 2008, Oracle and/or its affiliates. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Oracle or the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */ 


import java.security.*;
import java.security.spec.*;

public class SignatureVerifier {
	PublicKey publicKey;
	Signature sig;

	public SignatureVerifier(byte[] encodedKey){
		initPublicKey(encodedKey);
		createSignature();
	}

	/**
	 * create a Signature object and initialize it with the public key
	 */
	private void createSignature() {
		try{
		this.sig = Signature.getInstance("SHA1withDSA", "SUN");
		this.sig.initVerify(this.publicKey);
		} catch (Exception e) {
			System.err.println("Caught exception " + e.toString());
			e.printStackTrace();
		}
	}

	/**
	 * initializing the CA public key
	 * @param encodedKey
	 */
	private void initPublicKey(byte[] encodedKey) {
		// create a key factory
		KeyFactory keyFactory;
		try {
			keyFactory = KeyFactory.getInstance("DSA", "SUN");
		
		// create the pubKey according to the imported
		X509EncodedKeySpec pubKeySpec = new X509EncodedKeySpec(encodedKey);
		this.publicKey = keyFactory.generatePublic(pubKeySpec);
		} catch (NoSuchAlgorithmException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (NoSuchProviderException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (InvalidKeySpecException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

	/**
	 * Verifying matching between data and it's signature 
	 * @param data- the signed data
	 * @param signature- the signature
	 * @return true iff signature matches data
	 * @throws SignatureException 
	 */
	public boolean verify(byte[] data, byte[] signature) throws SignatureException{
		updateSignature(data);
		return this.sig.verify(signature);
	}


	/**
	 * add the given data to the signature object
	 * @param data- the data to add to the signature object
	 */
	public void updateSignature(byte[] dataToVerify){
		int offset = 0;
		int bytesLeft;
		bytesLeft = dataToVerify.length;
		while (bytesLeft > 0){
			if (bytesLeft > 1024){
				try {
					this.sig.update(dataToVerify, offset, 1024);
				} catch (SignatureException e) {
					System.err.println("Caught exception " + e.toString());
					e.printStackTrace();
				}
				offset += 1024;
				bytesLeft -= 1024;
			} else {
				try {
					this.sig.update(dataToVerify, offset, bytesLeft);
				} catch (SignatureException e) {
					System.err.println("Caught exception " + e.toString());
					e.printStackTrace();
				}
				offset += bytesLeft;
				bytesLeft = 0;
			}		
		}
	}
}




